Title

Author

Date of Award

2010

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Peter O. Koons

Second Committee Member

James Fastook

Third Committee Member

Brenda Hall

Abstract

The Greenland Ice Sheet, the sole remaining ice sheet in the Northern Hemisphere, is currently undergoing dynamic changes that have resulted in increasing mass loss. Representing 6-7 m of sea level equivalence, the Greenland Ice Sheet is of great interest to both the scientific community and society. Atmospheric variations are a major controlling aspect of continental glaciations and the health of ice sheets. The Greenland Ice Sheet is particularly exposed to the North Atlantic Oscillation (NAO), a well-known atmospheric fluctuation in sea level pressure between the Icelandic Low and Bermuda-Azores High. Persistence of a single phase of the NAO is known to cause significant changes in mass balance trends over the Greenland Ice Sheet that result in similar changes to the ice sheet. Quantitative estimates of these changes in ice thickness and volume, however, are lacking. NAO is chosen as a characteristic climate driver because it is an identifiable major modern atmospheric oscillation influencing temperature and precipitation over Greenland and may aid in predicting the future response of the Greenland Ice Sheet as well as improving the interpretation of its past. To investigate the Greenland Ice Sheet’s sensitivity to the NAO, numerical ice sheet modeling is utilized. The University of Maine Ice Sheet Model (UMISM) is used to develop a reconstruction of the present-day Greenland Ice Sheet driven primarily with modern-day atmospheric conditions and positive-degree-day mass balance calculations. These mass balance conditions and reconstructed ice sheet are then used to investigate the Greenland Ice Sheet’s sensitivity to persistent NAO phase conditions. Average surface temperature and total precipitation data from six distinctive years in the NAO record are used to drive persistent positive and negative NAO phase UMISM model runs. Comparisons to the reference mass balance conditions and ice sheet identify the resulting changes to the ice sheet (ice thickness and volume). Model runs are compared at temporally relevant intervals, representing observed average and extreme persistence of NAO phases. Results from the persistent positive and negative NAO phase UMISM model runs are applied to long-term reconstructed NAO records. Very long-term persistence of the positive NAO phase during the Medieval Warm Period (MWP) is linked to the settlement and establishment of farming communities by the Norse people in southwest Greenland. The disappearance of the Norse ~500 years later correlated with the subsequent weakening of the NAO signal and reestablishment of the negative NAO phase. The ice load changes associated with the behavior of the NAO result in lithospheric uplift (positive NAO) or subsidence (negative NAO), thus affecting the Norse people’s ability to maintain successful farming practices. The subsidence of the local bedrock during the reestablishment of the negative NAO phase occurs quickly (within a few decades) and at a modeled rate of ~3 mm/yr, which is in agreement with relative sea level observations. The resulting submergence and flooding of large sections of cultivatable land greatly affected the terrestrial resources available to the Norse and played a key role in their eventual disappearance.